[Qgis-user] Geomorphological microstructures 's footprint extraction?

[dandrigo]

Good morning,


We have as input a lidar point cloud (800 000 points) which is the result of
one our classification (this cloud represent only our geomorphological
structures class.) Then,from this cloud we generated a DTM (20cms).

Our goal is to delimit automatcally the footprint of these microstructures
with a polygonal vector. 

Pouvez vous nous éclairer sur les différentes méthodes et outils permettant
de faire celà? 
Could you throw light for us about methods and tools doing this task? 

Is it possible to capture this polygonal layer directly from the points
cloud? (hull).
Or would it be preferarable to work from the DTM raster or one of this
derivatived  (vector level curves, slope raster map, exposure raster map,
shading, etc.)? For instance, the slope raster map seems to be an
interesting criterion to identify and isolate the base of these
microstructures. Is would be possible to do an automatic vectorization?

Below, a screenshot showing the points cloud  and another showing  slope
raster :

<http://osgeo-org.1560.x6.nabble.com/file/n5311838/SS_cloud.jpg> 

<http://osgeo-org.1560.x6.nabble.com/file/n5311838/SS_raster_slope.jpg> 

Thank you very much for your usefull help.




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